1. Technical Field
The present invention relates to a vehicular display device having a display unit for displaying visible information and a light projection unit for reflecting light containing the visible information displayed on the display unit by a predetermined light reflection member to project the light to a predetermined observation region, and displaying the visible information as a virtual image.
2. Background Art
In a vehicular display device, a head-up display (HUD) having good visibility may be used to allow a driver to rapidly recognize information having, for example, a small information amount but a high degree of urgency.
The vehicular head-up display guides a light image, which contains visible information generally displayed on a display unit of a display device main body, onto a windshield (front glass) of a vehicle or a light reflection member, which is referred to as combiner, and projects an image of the reflected light to be seen by eyes of the driver.
Therefore, when the driver sees the front at a normal driving posture, the driver can visually recognize not only front scenery and a portion of the vehicle, which are transmitted and seen through the windshield, but also the visible information projected by the head-up display. The visible information which is visually recognized by the driver is imaged as a virtual image in front of a surface of the windshield, for example, at a several meter position distant from a viewpoint, and thus the driver can simultaneously recognize the front scenery and the display contents of the head-up display without focusing the eyes during driving.
This head-up display device is generally configured so that a device main body thereof is disposed in an instrument panel of the vehicle. The light of the visible information which is displayed on the display unit in the device main body is projected towards a projection area, such as a windshield or a combiner, via a light path including a reflection member, such as an enlarging system mirror, so that a virtual image is imaged at a predetermined position distant from the viewpoint of the driver, when viewed from the viewpoint.
The related art of the vehicular head-up display device is disclosed in JP-UM-H06-050952, for example. In JP-UM-H06-050952, there is proposed a head-up display device in which, in order to enhance visibility of information display, brilliance of a background of an information display portion is properly measured and correspondingly brilliance of the information display is optimally controlled. Also, there is disclosed a technique for integrally forming and arranging a light sensor, a light sensor driving transmission circuit and a solar cell in a room mirror.
In general, a vehicular head-up display device projects a light image so that a virtual image, which is seen from a viewpoint position of a driver, is imaged in front of a front windshield (front glass) of a vehicle. Thus, when seeing the front through the front windshield, the driver, who drives the vehicle, can visually recognize as a virtual image display contents of the head-up display device with overlapped with an object, such as front scenery or a portion (a bonnet or the like) of the vehicle.
However, for example, in a situation where a strong external light from the sun is arrived, such as daytime of a clear day, a light intensity of the external light becomes larger than that of the virtual image displayed by the head-up display device, and as a result, display of the virtual image is difficult to be visually recognized due to the influence of the external light. Therefore, as disclosed, for example, in JP-UM-H06-050952, optimally controlling brilliance of the information display may be effective to improve visibility.
Nevertheless, because the head-up display device performs display by the projected virtual image, when the intensity of the external light is very large, such as daytime of a clear day, the influence of the external light is too strong even if the light intensity of the virtual image is increased. As a result, it is impossible to ensure a sufficient visibility.
Therefore, it may be also contemplated to project the virtual image to a location other than the front of the front windshield in order to avoid the influence of the external light. However, if the virtual image is projected to such a location, the driver has to increase movement of the viewpoint or needs focusing of the eyes to see the virtual image, and thus a function as the head-up display device cannot be sufficiently exhibited.
Accordingly, the present invention has been made keeping in mind the above problem, and an object of the invention is to provide a projection-type vehicular display device, in which a sufficient visibility can be ensured even upon an environment, where the influence of external light is large, and also, the need for viewpoint movement and focusing of a driver can be reduced.